The present invention relates to a mounting of a rack-and-pinion steering system for motor vehicles and, more particularly to a mounting for passenger motor vehicles in which the track rods are arranged behind the axle in the direction of travel and in which a defined resilience of the rack mounting in the transverse direction of the vehicle is of particular importance to the behavior of the steering system.
The simplest form of a rack-and-pinion steering system of a motor vehicle is fastened by rigid bolting to frame or body parts, such as the front cross-member or the front bulkhead. In order to take vibrations and shocks transmitted via the wheels and wheel suspensions, elastic mountings for the rack-and-pinion steering system are used.
According to REIMPELL, Fahrwerktechnik-Lenkung, [translated: Running-gear technology--steering], Vogel-Verlag, 1984, mounting arrangements are known in which the rack-and-pinion steering system is elastically connected to the vehicle frame by a tubular damping rubber. A spacer tube integrated into the damping rubber prevents compression of the rubber body and also limits axial compressive stresses.
In, another known form, the casing of the rack-and-pinion steering system is almost completely surrounded by an elastomer body which is screwed into nonpositive engagement with the vehicle frame by fastening clips which engage therearound. The thick-walled elastomer body permits movements of the rack-and-pinion steering system in all three main spatial directions. This resilience of the steering system is however, undesirable, particularly in the longitudinal or travel direction of the vehicle and in a vertical direction because it leads to instability of the vehicle.
In addition, this known configuration involves considerable space requirements and, particularly in passenger motor vehicles, leads to design problems in the arrangement of the steering gear in the available region between the engine/gearbox unit and the stabilizer, taking into account the necessary ground clearance of the vehicle. Furthermore, an undesirable slewing or torsion movement of the rack-and-pinion steering system about its longitudinal axis is not completely prevented by the positive clip connection.
DE 37 04 412 shows a steering gear fastening having a plurality of shaped elastomer bodies which consist of a single part or two parts. The bodies are arranged in the longitudinal direction of the rack-and-pinion steering system. The identically shaped, homogeneous elastomer bodies enable only transverse forces to be absorbed. Similarly, a wheel suspension for steerable front wheels of a motor vehicle shown in DE 31 18 177 has a plurality of spaced shaped rubber parts which are arranged on the cross strut of the steering gear.
In DE 24 21 498, a U-shaped elastomer body is described and, with the aid of a peripheral tension band, permits slight axial movability of the rack-and-pinion steering system. This arrangement does not, however, permit automated installation of the completed rack-and-pinion steering system on the vehicle.
EP 0 351 146 shows a rack mounting which consists of a plurality of "silentblocs" in the form of hollow cylinders. This embodiment permits only slight resilience in the transverse direction of the vehicle, and thus does not allow the deflection of the mounted rack-and-pinion steering system which is necessary for under-steer of the vehicle.
EP 0 107 781 describes a plurality of asymmetrically () shaped multipart elastomer mounting bodies for the elastic mounting of a rack-and-pinion steering system. The spring elements subjected to compressive or shear stresses have a substantially annular shape. The elastomer parts, which together form a movable bearing and a fixed bearing, are connected to the vehicle body by holding straps gripping around, them. This mounting arrangement requires considerable space and does not permit automated installation on the complete assembly on the vehicle.
DE 34 25 730 shows a wheel suspension for a rear axle carrying steerable wheels and has a total of four asymmetrically arranged profiled rubber bodies spaced apart from one another. Two mountings arranged horizontally in the direction of travel serve to take longitudinal forces, while the two silentblocs arranged transversely to them take the resultant transverse forces acting on the co-steering rear axle. This known construction, which is expensive with respect to design and installation techniques, likewise does not permit automated final installation of the completed vehicle steering system.
An object of the present invention is to provide a mounting for a rack-and-pinion steering system which, through a tautly seated steering system, ensures stable guiding of the vehicle in the travel direction to prevent the dreaded "wandering" of the vehicle.
Transversely to the direction of travel, that is in the longitudinal direction of the rack-and-pinion steering system, limited elasticity of the mounting construction is required, in order to ensure the desired understeer of the vehicle during cornering. In addition, when the track rods are inclined in relation to the axis of the rack during deflection and rebound movements, the suspension of the rack-and-pinion steering system should intercept obliquely directed forces such that tilting of the rack about the vehicle longitudinal axis and also twisting about its own axis are largely avoided. Moreover, the rack-and-pinion steering system of the present invention is now installable automatically on the vehicle from below.
The object of the present invention has been achieved by providing that the two bearing guides arranged upright in longitudinal and transverse directions of the motor vehicle and spaced apart in the longitudinal direction of the steering gear and connected to a casing of the steering gear. In the bearing guide, two bearing bodies tapering towards the center of the respective bearing guide are aligned with one another in a mirror image arrangement. The bearing bodies have through-holes in a longitudinal direction of the bearing guide, and a damping element is arranged on the outer periphery of the bearing body. A wall thickness of the damping element in the longitudinal direction of the motor vehicle is greater than a wall thickness in the transverse direction of the motor vehicle. An inner wall of the bearing guide is shaped in accordance with an external contour of the bearing bodies with damping elements, and opposing bearing bodies, with the associated damping elements, are clamped axially together with a defined initial stress when installed in the bearing guide.
The rack-and-pinion steering system is mounted by two bearings which are arranged upright and at a relatively great distance from one another at the ends of the steering gear casing. The two bearings consist essentially of the bearing holder which is joined to the steering gear and of two bearing bodies having damping elements. The bearing bodies are V-shaped or Y-shaped in longitudinal section and have axial through holes for the passage of the clamp bolts. One upper and one lower bearing body together with damping elements are arranged symmetrically and in alignment with one another in the top and bottom pares respectively of the bearing guide. The smaller end faces of the V-shaped or Y-shaped bearing bodies face one another.
Through the upright arrangement of the bearing bodies with their damping elements, the latter are subjected axially to compressive stress and at the same time also to shear stress. Thus, the desired great stiffness and spring hardness in the vertical direction and also in the longitudinal direction of the vehicle are achieved.
The softness of the bearings in the transverse direction of the vehicle is achieved through the fact that the damping elements of the bearings are provided on their periphery, in the longitudinal direction of the steering gear, with depressions or flats on one side or diametrically opposite on both sides. A damping element flattened on both sides in the transverse direction of the vehicle is shown in FIG. 2 where the bearing gap on both sides in the transverse direction of the vehicle in the static state can be clearly seen. During cornering, this configuration permits soft deflection of the rack-and-pinion steering system. With correspondingly great forces the damping element makes contact over its entire surface with the inner wall of the bearing guide and is automatically centered by the bearing guide. Because of the greater spring hardness, further swinging-out of the rack-and-pinion steering system in the transverse direction of the vehicle is prevented.
Flattening of the damping element on one side is likewise shown solely by way of example in FIGS. 7 and 8. Using, on both sides, this kind of damping element, which has outwardly directed flats, in both the bearings brings about an initially steeper rise of the characteristic line of the spring force in the transverse direction of the vehicle. After a short spring travel, the lifting-off of the unloaded side produces a flat pattern of spring force over the spring travel, with a nearly linear rise.
This spring characteristic at first causes around the middle position a better stability of the vehicle and gives the driver the impression of driving with steering stability. Only when transverse forces become greater does the soft spring characteristic of the damping elements then occur, thus permitting the desired understeer of the vehicle. The V-shaped or Y-shaped configuration of the bearings offers the further advantage that obliquely directed supporting forces, which act on the steering gear via the track rods, are more effectively introduced.
Effective supporting of the rack-and-pinion steering system against tilting about the longitudinal axis of the vehicle is achieved through a large support base, in that in an advantageous embodiment the two bearings are arranged at a correspondingly great distance from one another on one longitudinal side of the rack casing.
In order to automate the installation of the rack-and-pinion steering system on the vehicle, the steering system is mounted on a mounting member, which in a preferred embodiment is in the form of a substantially C-shaped, beaded metal sheet. The mounting member receives the entire unit and is brought from below against the vehicle body. The bearings are taken to mounting holes in a cross-member and then bolted to the latter. This mounting bolting achieves at the same time the desired axial initial stress of the one-piece elastomer bodies which are preferably used damping elements for the two bearings in order to adjust the desired bearing hardnesses of the latter.
According to another aspect of the present invention, the bearing body is in the form of a truncated cone which is provided with a through hole and has a V-shape in longitudinal section. Through the mirror-image arrangement of two V-shaped bearing bodies aligned with one another, whose smaller end faces lie opposite one another, extremely small overall heights of the bearings can be achieved. In addition, because of their simple shape the bearing bodies are easy to produce in terms of the manufacturing technology involved.
In another aspect of the present invention, the bearing body is in the form of a truncated cone which is provided with a through hole and has a Y-shape in longitudinal section and which is provided with a hollow cylindrical extension on its smaller end face. The mirror-image arrangement of two Y-shaped bearing bodies lying with their smaller end faces aligned opposite one another offers the advantage that obliquely directed reaction forces on the steering gear, which forces occur in particular in the event of a large angle of lock (cornering, manoeuvering), can be dependably absorbed.
In an advantageous embodiment of the present invention, the damping element is in the form of a one-piece elastomer body which can be produced in a simple manner and is joined to the bearing body by elastic initial stress. Alternatively, the damping element is vulcanized to the bearing body.
In a currently preferred embodiment, the damping element is shaped to form on its periphery or end face a sealing lip which, in the installed state, is applied with a positive fit to the bearing guide and forms a dustproof covering for the bearing interior.
In order to ensure great bearing stability of the rack-and-pinion steering system in relation to tilting movements transversely to the longitudinal direction of the vehicle, the two bearings are arranged at the outer-most end points of the steering gear casing. When the steering gear casing is constructed in the form of a pressure diecasting, the bearing guides can in a simple manner be integrated into the wall of the casing.
To ensure automated installation of the steering system use is made of a mounting member which receives the preassembled rack-and-pinion steering system and, in an advantageous development is at the same time configured to protect the steering system against thrown-up stones and as underclearance protection.
It is particularly advantageous that the solution provided by the present invention makes possible achievement of a defined spring characteristic of the steering arrangement in the x-, y- and z-directions. This is accomplished through the different configuration of the bearing bodies and damping elements in conjunction with the adjustable initial stress of the spring system in the installation of the unit.
In addition, the arrangement of the present invention offers the advantage that, particularly on the rebound of the vehicle or with a large lock angle, the geometrically defined position of the steering gear relative to the other elements of the steering arrangement is retained. This results from the greater spring hardness in the x- and y-directions which prevents deflection of the rack-and-pinion steering system, whereas in the y-direction a defined deflection can occur. Because of the arrangement selected, however, torsion of the rack-and-pinion steering system about the y-axis is impossible.